The present invention relates in general to crash attenuators, and more particularly to medium-damped crash attenuators that use the flow of a medium such as a liquid or gas to dissipate the energy of an object such as a vehicle impacting the crash attenuator. It also relates in some cases to attenuators which use the controlled deformation of metal to absorb energy and thus damp the motion of the attenuator. Still more particularly, the invention relates to attenuators enabling active control of the rate of energy dissipation thereof to better control the deceleration of vehicles impacting the attenuator having widely varying kinetic energy.
The present invention also relates to method for protecting fixed structures from damage caused by the impact of objects such as vehicles, for example, structures situated alongside highways.
Many commercial products exist and numerous patents have been issued directed to the design and construction of impact attenuators or barriers to control the deceleration of an errant vehicle as it approaches an obstruction or hazard on, or adjacent to, a highway. Several prior art patents will be discussed below. This invention is concerned primarily with impact attenuators that are mounted on the rear of a construction vehicle, commonly called truck-mounted attenuators (TMA), although it is not limited thereto. The invention also has applicability to more permanent attenuator installations such as those of the type used around fixed highway structures especially where space is limited.
A review of some patents and commercial literature of TMAs illustrates a wide variety of designs which appear to have evolved by trial and error with little attempt to optimize the design to handle a wide variety of impacting vehicle kinetic energies. Thus, such existing devices generally have a fixed force versus deflection function that provides the same resisting force to the impacting vehicle regardless of that vehicle""s mass or velocity.
The primary purpose of a TMA is to protect construction personnel from death or injury caused by a vehicle which mistakenly or accidentally intrudes into a construction zone. Secondarily, the TMA is designed to minimize the death and injury to the occupants of the errant vehicle. Ideally, the TMA should capture the impacting vehicle preventing it from being diverted either into adjacent traffic or off the road where it might impact a roadside structure such as a utility pole. Preferably, the TMA should even decelerate the vehicle at an acceptable level, such as 15 Gs, regardless of the mass or velocity of the impacting vehicle. Additionally, it is desirable for the TMA to be low cost, reusable after an impact, easily transported, light weight, easily shipped, easily stored, etc. No TMA on the market today satisfactorily meets all of these requirements. Therefore, there is a dire need for such a TMA that is the subject of this invention.
It is clear from the patents and commercial literature that many mechanisms exist for absorbing energy of an impacting vehicle into a TMA. These include a variety of structures that depend on the bending of metal or plastic, devices that utilize water, foam rubber, plastic etc. in a variety of energy absorption modes. Frequently, the energy dissipated by the system is part of the structure of the device. In fact, the prior art inventions have frequently confused the functions of structure and energy absorption. The instant invention therefore centers on the separation of these two functions of supporting structure and energy dissipation and optimizing these functions separately.
The basic problem to be solved by a TMA design is to capture an impacting vehicle and preferably to decelerate it at an approximate constant value that is relatively independent of the velocity and mass of the impacting vehicle. It is also desirable for the impactor to be resetable and that it can be easily collapsed for transportation, shipping, storage etc. It is noteworthy that none of the TMAs on the market today are reusable and therefore invariably require replacement after an impact.
Review of the Prior Art:
U.S. Pat. No. 3,674,115 to Young et al. describes a liquid filled shock absorber comprised of many tubes each with a fixed orifice. On impact of a vehicle into the shock absorber, the fluid is forced to flow through the orifices which provides the energy dissipation. Since the orifices are fixed, the system will not adjust to vehicle impacts of varying kinetic energy to provide a constant deceleration. Also, since the device is substantially composed of such cylinders, it is heavy if used as a TMA. It is designed, therefore, for use in fixed installations.
U.S. Pat. No. 4,190,275 to Mileti describes a light weight reusable TMA which is self restoring and thus immediately available to receive an additional impact. The impact attenuator is constructed from a plurality of expanded plastic sheets sandwiched between plywood stiffeners. The expanded plastic sheets form air filled cells. The energy dissipation mechanism is not disclosed but it appears that the energy is stored as compressed gas within the cells rather than dissipated. Thus, there is a substantial force at the end of the crash to cause the impacting vehicle to change its direction and rebound at a substantial velocity off of the TMA thus substantially increasing the velocity change of the vehicle above the initial vehicle impact velocity. This increases the severity of the crash and thus the potential for injury to the construction crew and the vehicle occupants. There is no provision in this patent to adjust the force on the impacting vehicle so that substantially the same deceleration is achieved for vehicles of different kinetic energy. This has the effect of substantially increasing the length required of the device in order to handle both light and heavy impacting vehicles at high velocities. The first part of the TMA must be designed to decelerate a light, high speed vehicle at a safe level. This same force is then all that is available for the heavy vehicle which is then decelerated at a much lower level during the initial part of the crush and then at a higher level later.
U.S. Pat. No. 4,635,981 to Friton describes an attenuator including a series of chambers made from sheet metal with some of the chambers containing crushable plastic foam, which, along with the plastic deformation of the sheet metal, dissipates the kinetic energy of the impacting vehicle. The system is not reusable and does not adjust to impacting vehicles having different kinetic energies.
U.S. Pat. No. 4,674,911 to Gertz describes a crash cushion which uses the compression of air to act as a spring to provide an ever increasing force acting against the impacting vehicle. This system is reusable but does not adjust to impacting vehicles having different kinetic energies. By having the function of an ever increasing force with displacement, it is particularly inefficient in decelerating a vehicle where a constant force is desired.
U.S. Pat. No. 4,711,481 to Krage et al. describes an attenuator that uses the crushing or plastic deformation of sheet metal to provide the energy dissipation. This system is not reusable and does not adjust to impacting vehicles having different kinetic energies. By having the function on an ever increasing force with displacement, it is particularly inefficient in decelerating a vehicle where a constant force is desired.
U.S. Pat. No. 5,052,732 to Oplet et al. describes an attenuator which uses a plurality of layers of fibrous hexagonal elongate cells which provides energy absorption during crushing. It suffers from the same defects at Krage et al. (U.S. Pat. No. 4,711,481).
U.S. Pat. No. 5,101,927 (Murtuza) describes an automatic brake actuation device including a xe2x80x9cfeelerxe2x80x9d which extends forward of a vehicle and detects objects that the vehicle is about to strike. Upon detecting an object, the device actuates the brakes of the vehicle to bring the vehicle to rest. Also, upon impact with the object, the feeler is retracted without applying any force against such retraction. One stated object of the Murtuza invention is to provide an improved automatic brake actuation system wherein the extendable detector is retracted upon impacting an object. More particularly, in the embodiment shown in FIGS. 13 and 14, the device includes a support member 112 mounted to the vehicle and a feeler cylinder 114 having a piston 118 therein. Movement of the piston 118 controls expansion and retraction of a parallel-bar expanding feeler 130. Movement of the piston is obtained by forcing fluid into a retracting portion 128 of the cylinder 114 while fluid is vented from the extending portion 126 and vice versa. This is achieved by providing fluid controls to act as extending means or devices and retracting means or devices for supplying fluid under pressure to the feeler cylinder.
U.S. Pat. No. 5,192,157 to Latumer describes a fixed installation vehicle crash barrier that attempts to make use of a more efficient method of deforming metal to absorb energy. It also suffers from the same limitations as Krage et al. (U.S. Pat. 4,711,481).
U.S. Pat. No. 5,199,755 to Gertz describes a TMA that also uses the bending of metal as the main energy absorption mechanism and thus has the same limitations as Krage et al. (U.S. Pat. 4,711,481).
U.S. Pat. No. 5,403,112 to Carney describes a TMA where part of the structure is a scissors mechanism. The bending of metal is the energy absorption mechanism and thus has the same limitations as Krage et al. (U.S. Pat. 4,711,481).
U.S. Pat. No. 5,642,792 to June describes a TMA using large drum shaped plastic cylinders to provide an energy absorption system. The system is not reusable and does not adjust to the kinetic energy of the impacting vehicle.
U.S. Pat. No. 6,189,941 to Nohr, although not a TMA, describes a novel collapsing tube energy absorbing mechanism that is applicable to the invention disclosed herein for those cases where the variable damping feature is sacrificed for a lower cost system. This patent is incorporated by reference herein in its entirety and its teachings are particularly relevant to the invention disclosed herein.
Accordingly, none of the prior art patents mentioned above discloses a TMA having the sought after properties and thus, a critical need exists for such a device. A central issue is that since prior art TMAs are not optimally designed, they must be made very long in order to handle both low and high mass vehicles at high speed. This makes the devices expensive, difficult to maneuver and less than optimum as a life saving device.
It is an object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure.
It is another object of the present invention to provide a new and improved crash attenuator for mounting on a truck of stationary structure which is reusable.
It is another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which adjusts to the kinetic energy of a vehicle impacting into the same.
It is still another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which is efficient in decelerating a vehicle impacting into the attenuator where a constant deceleration is desired.
It is yet another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure that separates the functions of the supporting structure and the energy dissipation and optimizes these functions separately.
It is another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which enables active control of the rate of energy dissipation in order to better control the deceleration of vehicles impacting the attenuator having widely varying kinetic energy.
It is a further object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which is low cost, reusable after an impact, easily transported, light weight, easily shipped and easily stored.
It is an additional object of the present invention to provide a particularly low cost passive attenuator which does not require sensing and adjustment of the damping during the crash event.
The crash attenuators in accordance with this invention are first designed as a structural mechanism which is capable of supporting the loads arising from the impact of a vehicle and the resulting reaction loads arising from the truck inertial loading and the energy dissipation or damping device. The damping device is then designed which may be either one or more hydraulic cylinders, and/or one or more inflatable/deflatable airbags, and/or one or more controlled metal deformation mechanisms. This separates the structural function from the energy dissipation function and permits the optimization of each separately. In all three cases, a movable displacement structure is provided to enable movement of a bumper having an impact-receiving face toward and away from a frame connected to the truck or stationary structure. The displacement structure may comprise a scissors mechanism that has an expanded condition in which the bumper is distant from the frame and a contracted condition in which the bumper is relatively close to the frame. Similar scissors mechanisms have found a successful application for cases of load lifting in industrial settings. The energy dissipation device is coupled to the scissors mechanism and can be either hydraulic, pneumatic, or based on the deformation of metal, although the hydraulic design is preferred for most applications.
When based on the deformation of metal, i.e., deformation energy absorption means are coupled to the displacement structure for dissipating at least some of the impact energy of the object received by the bumper which causes the displacement structure to be moved from the first position toward the second position and thereby reducing the velocity of the object. Such deformation energy absorption means may comprise at least one deformable member is deformed upon movement of the displacement structure from the first position toward the second position with such deformation causing dissipation of impact energy of the object received by the bumper. The deformable members may be in the form of solid rods, hollow tubes, with such rods or tubes having non-specific cross-sections, e.g., circular cross-section, oval cross-section, square cross-section, etc. The deformation energy absorption means may further comprise a die assembly having a respective aperture through which each deformable member is forced. Multiple die assemblies can be provided, e.g., one die assembly for each deformable member or one die assembly for each pair of deformable members.
To enable deformation of cylindrical members, the apertures may have a smaller diameter than the diameter of the respective member being forced therethrough. The diameter may be controlled to vary in order to thereby vary the dissipation force. A smaller diameter aperture will provide a greater dissipation force relative to a larger diameter aperture for the same diameter member, with both smaller and larger diameter apertures being smaller than the diameter of the member. In addition to or instead of enabling deformation by providing a smaller diameter, the apertures can have a different shape than the rods, e.g., cylindrical rods with oval-shaped apertures.
If the members have a square or rectangular cross-section, then the apertures can also have a smaller square or rectangular cross-section, respectively, and optionally a different shape.
An expansion arrangement is provided to displace the displacement structure from the second position to the first position. To this end, a hydraulic cylinders may be positioned between the frame and a support rod connected to the die assembly. The hydraulic cylinder is arranged to freely allow movement of the displacement structure from the first position to the second position.
In a method for protecting a truck or fixed structure from damage resulting upon impact of a moving object with the truck or structure, a movable displacement structure is mounted to the truck or structure, the displacement structure having an expanded position and a contracted position, a bumper having an impact-receiving face adapted to receive the impact from the moving object is arranged on the displacement structure, and at least one deformable member is arranged in connection with the displacement structure and in a position in which it is caused to deform upon movement of the displacement structure from its expanded position to its contracted position. Such deformation is effective to dissipate at least some of the impact energy of the moving object and reduce the velocity of the moving object.
When members having a circular cross-section are used, a die assembly having a respective aperture having a smaller diameter than the diameter of the member is provided such that deformation of the member is caused by forcing the member into the respective aperture. The dissipation force is then controlled by varying the diameter of the respective aperture. Another die assembly can have apertures having a different shape than the shape of the members such that deformation of the members is caused by forcing the member into the respective aperture.
The properties of the member can also be selected appropriately to provide for a desired dissipation force.
When the deformation of metal is used herein, it must be understood that use of metal is not intended to limit the scope of the invention and other materials which exhibit similar properties as metal may also be used in the invention.
This approach was only partially implemented in U.S. Pat. No. 5,248,129 to Gertz wherein a scissors mechanism is coupled with energy absorbing elements and in U.S. Pat. No. 5,642,792 to June wherein a hinged support frame supports an energy absorbing rectangular box-like structure. A preferred design of a crash attenuator in accordance with the invention combines a scissors or other expandable structure containing a plurality of sections, preferably at least three or four sections, with hydraulic damping cylinders. In a second design of a crash attenuator in accordance with the invention, the scissors mechanism houses at least one inflatable airbag which may be in the form of an accordion structure with the various sections of the airbag internally tethered for shape retention. Other shape retention means may also be provided in connection with the airbag(s). In third design of a crash attenuator in accordance with the invention, a design similar to the hydraulic design is used with the hydraulic cylinders replaced with collapsing metal deformation energy dissipation devices.
An electronic control module may be incorporated onto the scissors mechanism in order to sense the motion of an impacting vehicle and control the opening of exhaust orifices associated with the hydraulic, the pneumatic energy dissipation device, or the metal deformation energy dissipation device in order to achieve a substantially constant deceleration of the vehicle regardless of the mass and velocity of the impacting vehicle. The cross section area of the airbag(s) will be made as large as possible in the pneumatic case in order to minimize the initial compression of the airbag(s) before maximum pressure is obtained. The motion sensing system may be ultrasonic, radar or lidar based, or preferably accelerometer based. An electronically controlled valve is used to control the flow of either the hydraulic fluid or other medium from hydraulic cylinders in the hydraulic case, or gas or other medium out of the airbag(s) for the pneumatic case, during impact. A motor controlled die can be used to perform a similar function for the metal deformation design.
The system functions as follows. In the collapsed state, the TMA will occupy a space of typically approximately 25% of its expanded state making it easy to transport, store and ship. It could occupy any amount less than about 50% of its expanded state. This is facilitated by the use of a scissors mechanism comprises linked members articulated to one another. Upon arrival at the work site, a hydraulic pump in the hydraulic or metal deformation cases, or small vacuum cleaner type pump for the pneumatic case, can be activated to expand the TMA to its extended state where it is ready to receive an impact. The scissors mechanism will thus be expanded as the hydraulic pump is actuated to extend pistons associated therewith, the cylinder and piston of each hydraulic cylinder being connected to different parts of the scissors mechanism, or the airbag(s) is(are) inflated.
Bumpers at the end of the TMA, made from a material such as polyurethane foam, provide a low level of energy absorption for low speed impacts. At higher speeds, a deformable sub-bumper structure can be used to help channel the vehicle into the center of the TMA and capture it to prevent it from being deflected off of the TMA. In some cases, no compliant bumper is used and the bumper is a rigid metal plate. Accelerometers can be located in the rear of the bumper structure to sense the deceleration of the bumper, and thus the deceleration of the impacting vehicle. These accelerometers can send signals to a control module, which then adjusts the valve or orifice openings to control the fluid outflow from the hydraulic cylinders or medium outflow from the airbag(s), or the opening of a die or other similar mechanism for the metal deformation case, and thereby vary the energy dissipation force provided by the energy dissipation device and as a result, the vehicle deceleration. In the hydraulic embodiment, the rate of fluid outflow will be reflected in the movement of the piston back into the cylinder. In this manner, the system will provide a large energy dissipation force when the impacting vehicle is a heavy vehicle and a lower energy dissipation force for light vehicles, thus approximately stopping both types of vehicles in the same distance for the same velocity of impact. This permits a more efficient utilization of the available crush space and thus minimizes the size of the TMA. A similar function can be provided in the metal deformation case.
Some loss of efficiency results from the initial compressibility of the gas in the airbag for the pneumatic case. However, calculations set forth in Appendix 1 show that this loss of efficiency is manageable without greatly increasing the length of the TMA if atmospheric pressure is used. To the extent that the airbag can be pressurized, this effect will become smaller. Other energy absorption mechanisms, such as those using the deformation of metal as discussed below, that provide a force in parallel at least during the compression stage can of course be added to help compensate for this compressibility effect.
Another concern of the pneumatic system is in the compliance of the airbag itself. Once again, calculations indicate that this should not be a significant problem if the airbag is properly designed. In some cases, an accordion design with simple tethering will prove to be insufficient and a design based on a self-shaping airbag design, as disclosed in U.S. Pat. No. 5,653,464 incorporated herein by reference, which solves the problem by properly shaping the airbag to cause it to naturally take on the desired shape.
Although the preferred design uses electronics to control the energy absorption system, such as the valve associated with the hydraulic cylinders or orifice opening(s) associated with the airbag(s), other variations include the use of a mechanical system to sense the acceleration and control the opening of the flow restrictors, i.e., the valve or orifice openings. This results in an all-mechanical system by eliminating the electronics. The all-mechanical system is particularly applicable for fixed installations in addition to truck mounted applications.
In one method for protecting a truck or fixed structure in accordance with the invention, a movable displacement structure is mounted to the truck or structure and has an expanded position and a contracted position. A bumper having an impact-receiving face adapted to receive an impact from an object in a crash is arranged on the displacement structure. The displacement structure is preferably stored and transported in its contracted condition and when readied for use, it is expanded to its expanded position. In use, impact of an object into the bumper which causes the displacement structure to be moved from the expanded position toward the contract position is sensed and at least some, if not all, of the impact energy of the object is dissipated by adjusting an energy dissipation force such that the object is brought to rest. In some preferred embodiments, the displacement structure may be expanded after the impact energy of the object is dissipated such that the crash attenuator is reusable.
It is possible to sense deceleration of the object after impact into the bumper and adjust the energy dissipation force based on the sensed deceleration of the object. The hydraulic, pneumatic and metal deformation systems described herein may be applied.